1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine or, in particular, to a control apparatus for an internal combustion engine including an electronically controlled throttle valve in which the air-fuel ratio is controlled by the intake air amount followed by the fuel supply amount.
2. Description of the Related Art
In a conventional internal combustion engine of electronically-controlled fuel injection type, the intake air amount is measured and the fuel injection amount conforming with the intake air amount thus measured is calculated thereby to adjust the air-fuel ratio. This method of adjusting the air-fuel ratio is based on the concept that the intake air amount is determined according to the amount of actuation of the accelerator pedal. As a result, at the time of engine acceleration or deceleration when the intake air amount undergoes a considerable change, the problem is posed that an error is liable to develop in the intake air amount measured by the computer for controlling the engine.
In view of this, an engine control apparatus of fuel-amount-first air-amount-second control type is disclosed in JP-B-7-33781 using an electronically controlled throttle valve controlled by an electric actuator in accordance with the amount of actuation of the accelerator pedal, in which the amount of fuel injected (fuel injection amount) is determined first and then the intake air amount.
In the engine control apparatus according to JP-B-7-33781 of an engine of fuel-amount-first air-amount-second control type for controlling adjusting the fuel supply amount and the throttle valve opening degree in accordance with the accelerator pedal operating position, a technique is disclosed in which a predetermined delay time before fuel is actually taken into the cylinder is set in controlling the throttle valve opening degree to control the fuel supply amount in accordance with the engine rotational speed and the operating position of the accelerator pedal.
By setting a delay time in this way, the time before the injected fuel is actually taken into the cylinder is taken into consideration so that the fuel amount and the intake air amount in the cylinder are controlled accurately.
In view of the fact that the engine operating condition actually changes frequently and the calculated delay time is varied with the engine rotational speed or the fuel injection amount, however, the engine control apparatus disclosed in JP-B-7-33781 poses the problem that the throttle valve sometimes cannot respond to such a change, especially at the time of sudden operation of the accelerator pedal. It is thus difficult to control the throttle valve opening degree to a target value based on each throttle valve opening degree, thereby making it impossible to always determine an accurate air-fuel ratio.